Stilbene compound, intermediate for producing the stilbene compound, method of producing the stilbene compound, and liquid crystal composition containing the stilbene compound

ABSTRACT

An optically active stilbene compound of formula (I): ##STR1## wherein R is an alkoxy group with 20 or less carbon atoms; n is an integer of 1 or 2; and R* is an optically active group, a substituted benzylphosphonate compound of formula (II) serving as an intermediate for preparing the above active stilbene compound, ##STR2## wherein X represents ##STR3## R&#39; is an alkyl group having 1 to 5 carbon atoms, or an unsubstituted or substituted aryl group; and R* is the same as in formula (I), a method of producing the optically active stilbene compound of formula (I), and a liquid crystal composition containing the optically active stilbene compound of formula (I) are disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optically active stilbene compoundused as a liquid crystal material; to an intermediate for, and to amethod for producing the optically active stilbene compound; and to aliquid crystal composition containing the optically active stilbenecompound.

2. Discussion of Background

At the present time, liquid crystal materials are widely used as displayelements. Almost all these liquid crystal display elements, however, arethe TN (Twisted Nematic) type of display systems which utilize nematicliquid crystals. This type of liquid crystal display element has thedrawback that its response speed is low, inasmuch as the response speedsobtained are in the order of several seconds, at the best.

For this reason, various types of liquid crystal display systems basedon other principles have been tried in place of the TN display system.One such system uses a strongly dielectric liquid crystal material (N.A. Clarks et al.; Applied Phys. Lett. 36, 899 (1980)). This system,which uses a strongly dielectric chiral smectic phase, and, inparticular, a chiral smectic C phase, is attracting considerableinterest as a high speed optical switching device. This type of highlydielectric liquid crystal material is already well known, for example,as disclosed in Japanese Laid-Open Patent Application 64-70455, but doesnot adequately provide the desired characteristics.

SUMMARY OF THE INVENTION

Accordingly, a first object of the present invention is to provide anoptically active stilbene compound which adequately demonstrates thecharacteristics, such as high response, and chemical stability, desiredin a liquid crystal material suitable for an optical switching system.

A second object of the present invention is to provide an intermediateto be used in the production of the optically active stilbene compound.

A third object of the present invention is to provide a method ofproducing the optically active stilbene compound.

A fourth object of the present invention is to provide a liquid crystalcomposition containing the optically active stilbene compound.

The first object of the present invention is achieved by an opticallyactive stilbene compound as represented by the following formula (I)##STR4## wherein R is an alkoxy group with 20 or less carbon atoms; n isan integer of 1 or 2; and R* is a optically active group.

The second object of the present invention is achieved by a substitutedbenzylphosphonate compound with the following formula (II): ##STR5##wherein X represents ##STR6## R* is an optically active group with 20 orless carbon atoms, R' is an alkyl group having 1 to 5 carbon atoms, suchas a methyl group, an ethyl group, and a butyl group, or anunsubstituted or substituted aryl group.

The third object of the present invention is achieved by a method ofproducing the optically active stilbene compound of the previouslymentioned formula (I) by the reaction of the above-mentioned substitutedbenzylphosphonate of formula (II) and an aldehyde as represented by thefollowing formula (III): ##STR7## wherein R is an alkoxy group with 20or less carbon atoms; and n is an integer of 1 or 2.

The fourth object of the present invention is achieved by a liquidcrystal composition containing the optically active stilbene compound asrepresented by the above-mentioned formula (I).

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 to FIG. 3 are IR spectra of the stilbene compounds according tothe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The stilbene compound of the present invention represented by formula(I) exhibits characteristics which are extremely useful as a liquidcrystal material which must have a high response speed, superiororientation, and the like, as well as photochromic characteristics. Itcan therefore be used as a reversible optical memory. Specifically, thisreversibility can be controlled by light, either over the entire surfaceor at an optional portion, because the structure of the material changesreversibly from the transform to the cis form where the cis formexhibits no liquid crystal characteristics at a certain specificwavelength λ₁, and from the cis form to the transform where thetransform exhibits liquid crystal characteristics at another wavelengthλ₂.

The compounds represented by formula (I) are generally obtained by thereaction of a substituted benzylphosphonate compound, represented byformula (II), with an aldehyde, represented by formula (III), using ametal alkoxide such as sodium methoxide, sodium ethoxide or potassiumt-butoxide, or a base such as sodium hydride, as a catalyst, at atemperature in the room temperature to 100° C. range. Solvents used areether-type solvents such as diethylether, tetrahydrofuran,dimethoxyethane, and the like, alcohols such as methanol, ethanol, andthe like, or amides such as dimethylsulfoxide and the like.

The compound represented by formula (II) may be reacted with thecompound represented by formula (III) in a stoichiometric mole ratio.

The compound represented by formula (II) can be obtained, for example,in accordance with the following reaction scheme: First, 4-methylbenzoicchloride of formula (IV) and an optically active alcohol of formula (V)ar reacted in the presence of a base such as pyridine to obtain anoptically active 4-methylbenzoic ester of formula (VI). Next, theoptically active 4-methylbenzoic ester of formula (VI) is converted tooptically active 4-alkoxycarbonylbenzyl bromide (VII) withN-bromosuccinimide, using a conventional method described, for example,in Org. Synth., IV 921 (1963). The compound represented by formula (II)can then be obtained from the optically active 4-alkoxycarbonylbenzylbromide (VII) and a tri-substituted phosphorous acid by means of aconventional method described, for example, in Chem. Rev., 74, 87(1972). ##STR8##

The optically active stilbene compound of the present inventionrepresented by formula (I) exhibits superior performance as a highlydielectric liquid crystal material. It has a high response speed, showsextremely good orientation, and is chemically stable.

The optically active stilbene compound of the present inventionrepresented by formula (I) can be used independently as a highlydielectric liquid crystal material, but it is possible to obtain acomposition with improved performance by mixing this stilbene compoundwith non-chiral smectic liquid crystals or with another highlydielectric liquid crystal material.

The addition of the optically active stilbene compound represented byformula (I) to nematic liquid crystals is effective in preventing theoccurrence of a reverse domain in the TN-type cells. In such a case, theoptically active stilbene compound of formula (I) is preferably used tothe extent of.0.01 to 50 wt % of the resulting composition.

In addition, by adding the optically active stilbene compound of formula(I) to nematic liquid crystals or to chiral nematic liquid crystals, thechiral nematic liquid crystals can be used as a liquid crystalcomposition in a phase-transition type or in a guest-host type liquidcrystal element. In this case, the optically active stilbene compound offormula (I) is preferably used to the extent of 0.01 to 80 wt % of theresulting composition.

The liquid crystal composition containing the compound of the presentinvention can be used for purposes other than display. It is suitablefor us in the field of optoelectronics in various optoelectronic devicessuch as optoelectronic shutters, optoelectronic diaphragms, opticalmodulators, optical communication path switches, memories,adjustable-focal-length lenses, and the like.

Among other liquid crystal compounds which can be used jointly with thecompound of the present invention, Table 1 gives examples of those whichexhibit a highly dielectric chiral smectic phase.

    TABLE 1        Phase Transition No. Chemical Formula Temperature (°C.)      1     ##STR9##      ##STR10##       p-decyloxybenzylidene-p'-amino-2-methylcinnamate      2     ##STR11##      ##STR12##       p-hexyloxybenzylidene-p'-amino-2-chloropropylcinnamate      3     ##STR13##      ##STR14##       p-decyloxybenzylidene-p'-amino-2-amino-2-methylbutyl-α-cinnamate      4     ##STR15##      ##STR16##       p-tetradecyloxybenzylidene-p'-amino-2-methylbutyl-α-cinnamate     5      ##STR17##      ##STR18##       p-octyloxybenzylidene-p'-amino-2-methylbutyl-α-chlorocinnamate     6      ##STR19##      ##STR20##       p-octloxybenzylidene-p'-amino-2-methylbutyl-α-chlorocinnamate     7      ##STR21##      ##STR22##       p-octyloxybenzylidene-p'-amino-2-methylbutylbenzoate      8     ##STR23##      ##STR24##       4,4-azoxycinnamic acid-bis(2-methylbutyl)ester      9     ##STR25##      ##STR26##       4-0-(2-methyl)-butylresorcilydene-4'-octylaniline      10     ##STR27##      ##STR28##       (2'-methylbutyl)-4'-octyloxybiphenyl-4-carboxylate      11     ##STR29##      ##STR30##       4-(2'-methylbutyl)phenyl-4'-octyloxybiphenyl-4-carboxylate  12      ##STR31##      ##STR32##       4-hexyloxyphenol-4-(2"-methylbutyl)biphenyl-4'-carboxylate  13      ##STR33##      ##STR34##       4-octyloxyphenyl-4-(2"-methylbutyloxy)biphenyl-4"-carboxylate  14      ##STR35##      ##STR36##       4-heptylphenyl-4(4"-methylhexylbiphenyl-4"-carboxylate      15     ##STR37##      ##STR38##       4(2"-methylbutyl)phenyl-4-(4"-methylhexyl)biphenyl-4'-carboxylate     SmC*: High Dielectric Smetic Phase C     SmA: Smetic Phase A     SmH*: High Dielectric Smetic Phase H     Sm3: Smetic Phase

Other features of this invention will become apparent in the course ofthe following description of the exemplary embodiments which are givenfor illustration of the invention and are not intended to be limitingthereof. Furthermore, it should be noted that there are slightdifferences between the measured values and the standard values for thephase transition temperatures of the examples, depending upon themeasurement method and the purity of the compounds tested.

EXAMPLE 1 [Preparation of 4-n-octyloxy-4'-[(S)-2-methylbutoxycarbonyl]Stilbene ##STR39## in which R=--OC₈ H₁₇, n=1, ##STR40## Step A-1.Preparation of 4-methylbenzoic acid [(S)-2-methyl

butyl)]ester ##STR41## in which ##STR42##

28.51 g (0.23 moles) of a commercially available (S)-2-methylbutanol wasdissolved in 100 ml of pyridine. The mixture was cooled and 50 g (0.23moles) of a commercially available 4-methylbenzoic chloride was addedthereto while cooling. The mixture was then allowed to react withstirring at 50° to 60° C. for 2 hours. On completion of the reaction,300 ml of water and 300 ml of toluene were added, and after vigorousstirring, the toluene layer was separated out and washed with 6N HCl.Washing was continued until this layer was neutral. This toluene layerwas dried with anhydrous magnesium sulfate, after which the toluene wasdistilled away. The residue was further subjected to evaporation underreduced pressure at 118° to 120° C. (5 mm Hg) and the distillaterecovered, whereby 59.61 g of the objective4-methylbenzoic((S)-2-methylbutyl) ester was obtained.

The thus obtained product was subjected to elemental analysis and theresult is as follows

    ______________________________________                                                    Found Calculated                                                  ______________________________________                                        % C           75.73   75.69                                                   % H           8.87    8.80                                                    ______________________________________                                    

Step B-1. Preparation of 4-[(S)-2-methylbutoxycarbonyl]benzylbromide##STR43## in which ##STR44##

20.63 g (0.1 mole) of the 4-methylbenzoic acid[(S)-2-methylbutyl]esterobtained in Step A-1, 17.80 g (0.1 mole) of N-bromosuccinimide, and 1.32g (0.005 moles) of benzoyl peroxide were dissolved in 120 ml of drycarbon tetrachloride and allowed to react under reflux for three hours.On completion of the reaction, the reaction mixture was filtered whilehot to remove the succinimide, which is a by-product of the reaction,and 27.70 g of a crude form of the objective 4-((S)-2-methylbutoxycarbonyl)benzylbromide was obtained from the filtrate byevaporating off the carbon tetrachloride.

Step C-1. Preparation of 4-[(S)-2-methylbutoxycarbonyl]benzyldiethylphosphate ##STR45## in which ##STR46## R' is --C₂ H₅, and

27.70 g of the 4-((S)-2-methylbutoxycarbonyl)benzylbromide obtained inStep B was added dropwise to 33.23 g (0.2 moles) of triethylphosphiteand the temperature of the mixture was gradually raised with stirring.The mixture was allowed to react at 140° to 150° C. for 4 hours. Oncompletion of the reaction, the mixture was subjected to evaporationunder reduced pressure at 190° to 193° C. (1 mm Hg) and the distillaterecovered, whereby 23.67 g of the objective4-((S)-2-methyl-butoxycarbonyl)benxyldiethylphosphate was obtained.

The thus obtained product was subjected to elemental analysis and theresult is a follows:

    ______________________________________                                                    Found Calculated                                                  ______________________________________                                        % C           59.48   59.64                                                   % H           7.80    7.95                                                    ______________________________________                                    

The chemical structure of this compound was also confirmed by infraredabsorption spectrum analysis. The infrared spectrum is shown in FIG. 1.

Step D-1. Preparation of4-n-octyloxy-4'-[(S)-2-methylbutoxycarbonyl)stilbene

3.42 g (0.01 mole) of the4-[(S)-2-methylbutoxycarbonyl]benzyldiethylphosphate obtained in Step C.was dissolved in 100 ml of dimethoxyethane, then 0.6 g (0.015 moles) of60% sodium hydride was added with stirring, after which 2.34 g (0.01mole) of n-octyloxybenzaldehyde was added dropwise over a five minuteperiod. The mixture was then allowed to react at room temperature for 2hours. On completion of the reaction, 200 ml of water and 200 ml oftoluene were added, and after vigorous stirring, the toluene layer wasseparated out and washed with 6N HCl. Washing was continued until thislayer was neutral. This toluene layer was dried with anhydrous magnesiumsulfate, after which the toluene was distilled away. A silica gel columnchromatography treatment was performed on the residue using toluene asthe developing solvent. The crude objective product obtained in thismanner was recrystallized three times from ethanol to obtain 2.22 g ofthe purified product. The optical rotation of this product, [α]^(D), wasfound to be +3.89° (chloroform), and the chemical structure of thiscompound was also confirmed by infrared absorption spectrum analysis.The infrared spectrum is shown in FIG. 2.

EXAMPLES 2 to 7

Liquid crystal compounds of Examples 2 to 7 shown in the following Table2 were obtained by a similar method to Step D-1 in Example 1, using thealdehydes represented by the general formula (III). The values for theelemental analyses and the phase transition temperatures for the liquidcrystal compounds of Examples 2 to 7 obtained in the above manner arealso given in Table 2.

                                      TABLE 2                                     __________________________________________________________________________     ##STR47##                                                                                  Elemental Analysis                                              Example                                                                            R      n Found (%)                                                                           Calculated (%)                                                                        Phase Transition Temperature                      __________________________________________________________________________                                (°C.)                                      1    n-C.sub.8 H.sub.17 O                                                                 1 C H                                                                             79.54  9.12                                                                       79.58  9.06                                                                            ##STR48##                                        2    n-C.sub.12 H.sub.25 O                                                                1 C H                                                                             80.21  9.61                                                                       80.29   9.69                                                                           ##STR49##                                        3    n-C.sub.10 H.sub.21 O                                                                1 C H                                                                             79.97  9.50                                                                       79.96  9.39                                                                            ##STR50##                                        4    n-C.sub.9 H.sub.19 O                                                                 1 C H                                                                             79.69  9.30                                                                       79.77  9.23                                                                            ##STR51##                                        5    n-C.sub.7 H.sub.15 O                                                                 1 C H                                                                             79.37  9.02                                                                       79.37  8.88                                                                            ##STR52##                                        6    n-C.sub.6 H.sub.13 O                                                                 1 C H                                                                             79.11  8.78                                                                       79.15  8.69                                                                            ##STR53##                                        7    n-C.sub.18 H.sub.21 O                                                                2 C H                                                                             82.01  9.01                                                                       82.09  8.80                                                                            ##STR54##                                        __________________________________________________________________________     Cryst. denotes crystalline state; Iso, isotropic liquid; S.sub.A, smectic     phase A; Sc*, chiral smetic phase C.                                     

EXAMPLE 8

[Preparation of 4-n-octyloxy-4'-[(R)-2-methylheptyloxycarbonyl]stilbene##STR55## in which R=--OC₈ H₁₇, n=1, ##STR56##

Step A-2. Preparation of 4-methylbenzoic acid [(R)-1-methylheptyl] ester##STR57## in which ##STR58##

40 g (0.31 moles) of a commercially available (R)-2-octanol wasdissolved in 100 ml of pyridine. The mixture was cooled and 47.93 g(0.31 moles) of a commercially available 4-methylbenzoic chloride wasadded thereto while cooling. The mixture was then allowed to react withstirring at 50° to 60° C. for 2 hours. On completion of the reaction,300 ml of water and 300 ml of toluene were added, and after vigorousstirring, the toluene layer was separated out and washed with 6N HCl.Washing was continued until this layer was neutral. This toluene layerwas dried with anhydrous magnesium sulfate, after which the toluene wasdistilled away. The residue was further subjected to evaporation underreduced pressure at 144° to 146° C. (2 mm Hg) and the distillaterecovered, whereby 70.37 g of the objective 4-methylbenzoic acid[(R)-2-methylheptyl]ester was obtained.

The thus obtained product was subjected to elemental analysis and theresult is as follows:

    ______________________________________                                                    Found Calculated                                                  ______________________________________                                        % C           77.42   77.38                                                   % H           9.65    9.74                                                    ______________________________________                                    

Step B-2. Preparation of 4-[(R)-1-methylheptyloxycarbonyl] benzylbromide##STR59## in which ##STR60##

24.84 g (0.1 mole) of the 4-methylbenzoic acid [R)-1-methylheptyl]esterobtained in Step A-2, 17.80 g (0.1 mole) of N-bromosuccinimide, and 1.32g (0.005 moles) of benzoyl peroxide were dissolved in 120 ml of drycarbon tetrachloride and allowed to react under reflux for three hours.On completion of the reaction, the solution was filtered while hot toremove the succinimide, which is a by-product of the reaction, and 31.40g of a crude form of the objective4-[(R)-1-methylheptyloxycarbonyl]benzyl bromide was obtained from thefiltrate by evaporating off the carbon tetrachloride.

Step C-2. Preparation of 4-[(R)-1-methylheptyloxycarbonyl]benzyldiethylphosphate ##STR61## in which ##STR62##

31.40 g of the 4-[(R)-1-methylheptyloxycarbonyl) benzylbromide obtainedin Step B-2 was added dropwise to 3.23 g (0.2 moles) oftriethylphosphite and the temperature of the mixture was graduallyraised with stirring. The mixture was allowed to react at 140° to 150°C. for 4 hours. On completion of the reaction, the excesstriethylphosphite was removed by distillation under reduced pressure,whereby 35.12 g of a crude form of the objective4-[(R)-1-methylheptyloxycarbonyl]benzyldiethylphosphate was obtained.

Step D-2. Preparation of4-n-octyloxy-4'-[(R)-2-methylheptyloxycarbonyl)stilbene

3.84 g (0.01 mole) of the 4-((R)-1-methylheptyloxycarbonyl)benzyldiethylphosphate obtained in Step C-2 was dissolved in100 ml of dimethoxyethane, then 0.6 g 0.015 moles) of 60% sodium hydridewas added with stirring, after which 2.34 g (0.01 mole) ofn-octyloxybenzaldehyde was added dropwise over a five minute period. Themixture was then allowed to react at room temperature for 2 hours. Oncompletion of the reaction, 200 ml of water and 200 ml of toluene wereadded, and after vigorous stirring, the toluene layer was separated outand washed with 6N HCl. Washing was continued until this layer wasneutral. This toluene layer was dried with anhydrous magnesium sulfate,after which the toluene was distilled away. A silica gel columnchromatography treatment was performed on the residue using toluene asthe developing solvent The crude objective product obtained in thismanner was recrystallized three times from ethanol to obtain 2.09 g ofthe purified product. The optical rotation of this product, [α]^(D), wasfound to be -41.56° (chloroform). The chemical structure of thiscompound was also confirmed by infrared absorption spectrum analysis.The infrared spectrum is shown in FIG. 3.

EXAMPLES 9 TO 15

Liquid crystal compounds of Examples 9 to 15 shown in the followingTable 3 were obtained by a similar method to the method in Step D-2 inExample 8, using the aldehydes represented by the general formula (III).The values for the element analyses and the phase transitiontemperatures for the liquid crystal compounds of Examples 9 to 15obtained in the above manner are also given in Table 3.

                                      TABLE 3                                     __________________________________________________________________________     ##STR63##                                                                                  Elemental Analysis                                              Example                                                                            R      n Found (%)                                                                           Calculated (%)                                                                        Phase Transition Temperature                      __________________________________________________________________________                                (°C.)                                       8   n-C.sub.8 H.sub.17 O                                                                 1 C H                                                                             80.09  9.65                                                                       88.13  9.54                                                                            ##STR64##                                         9   n-C.sub.12 H.sub.25 O                                                                1 C H                                                                             80.58 10.19                                                                       80.72 10.07                                                                            ##STR65##                                        10   n-C.sub.10 H.sub.21 O                                                                1 C H                                                                             80.33  9.92                                                                       80.44   9.82                                                                           ##STR66##                                        11   n-C.sub.9 H.sub.19 O                                                                 1 C H                                                                             80.21  9.83                                                                       80.29  9.69                                                                            ##STR67##                                        12   n-C.sub.7 H.sub.19 O                                                                 1 C H                                                                             79.83  9.56                                                                       79.96  9.39                                                                            ##STR68##                                        13   n-C.sub.6 H.sub.13 O                                                                 1 C H                                                                             79.63  9.35                                                                       79.77  9.23                                                                            ##STR69##                                        14   n-C.sub.10 H.sub.21 O                                                                2 C H                                                                             82.12  9.30                                                                       82.35  9.22                                                                            ##STR70##                                        15   n-C.sub.8 H.sub.17 O                                                                 2 C H                                                                             82.10  8.98                                                                       82.18  8.95                                                                            ##STR71##                                        __________________________________________________________________________     Cryst. denotes crystalline state; Iso, isotropic liquid; S.sub.A, smectic     phase A; Sc*, chiral smetic phase C.                                     

APPLICATION EXAMPLE 1

The surfaces of a pair of transparent electrode sheets were coated withpolyvinyl alcohol (PVA), after which the surfaces were rubbed for aparallel orientation treatment.

Test cells were prepared by positioning the two sheets in oppositionwith a space of 3 μm between them, with a PVA film on the inside. Theoptically active stilbene compound of Example 1 was then poured into thecell formed in this manner, after which the cell was placed between twosheets of polarizers in a cross-polarized orientation to obtain a liquidcrystal display element. When a potential of 30 volts was appliedbetween the electrodes, a good, clear contrast was obtained and aswitching action with a high response speed (about 150 μsec) wasobserved.

APPLICATION EXAMPLE 2

A liquid crystal composition A was prepared by mixing the followingcomponents with the following formulation: ##STR72##

The phase transition temperatures (° C.) of this composition were asfollows. ##STR73##

A pair of glass plates, on which an ITO film was formed as a transparentelectrode, were coated with Polyimide JIB-1 (manufactured by JapanSynthetic Rubber Co., Ltd.). The surfaces were rubbed for a parallelorientation, and test cells were prepared by positioning the glasssubstrates in opposition, separated by a space of 2 μm, with thepolyimide film on the inside, then joining the glass plates using anadhesive sealing agent (Trademark "Lixon Bond" manufactured by ChissoCorporation).

This cell was then filled with the previously prepared liquid crystalcomposition A in a uniform liquid state in the isotropic phase, afterwhich the filled cell was placed between two sheets of polarizer in across-polarized orientation to obtain a liquid crystal display element.At room temperature, when a potential of 20 volts was applied betweenthe electrodes, a good, clear contrast was obtained and a switchingaction with a high response speed (about 250 μsec) was observed.

The optically active stilbene compound of the present inventionrepresented by general formula (I) exhibits superior characteristics asa highly dielectric liquid crystal material. It has a high responsespeed, shows extremely good orientation, and is chemically stable.

The optically active stilbene compound of the present inventionrepresented by the general formula (I), when added to nematic liquidcrystals, is effective in preventing the occurrence of a reverse domainin TN-type cells.

Accordingly, the liquid crystal composition containing the compound ofthe present invention of the formula (I) can be used for purposes otherthan display. It is suitable for use in the field of optoelectronics invarious optoelectronic diaphragms devices such as optoelectronicshutters, optoelectronic, optical modulators, optical communication pathswitches, memories, focal-length-adjustable lenses, and the like.

What is claimed is:
 1. An optically active stilbene compound of theformula (I): ##STR74## wherein R is an alkoxy group with 20 or lesscarbon atoms; n is an integer of 1 or 2; and R* is an optically activegroup selected from the group consisting of 1-methylheptyl,2-methylheptyl and 2-methyloctyl.
 2. A method of producing an opticallyactive stilbene compound of formula (I) by the steps comprising reactinga substituted benzylphosphonate of formula (II) and an aldehyde offormula (III): ##STR75## wherein X is ##STR76## R' is an alkyl grouphaving 1 to 5 carbon atoms, or an unsubstituted or substituted arylgroup, R* is an optically active group selected from the groupconsisting of 1-methylheptyl, 2-methylheptyl and 2-methyloctyl, and n isan integer of 1 or 2.